Fix snail issue for all shipping method fees

[vsmay98]

What? Why?

Closes #8249

What should we test?

flat percent --> snail
flat rate (per order) --> OK
flexible rate --> snail
flat rate (per item) --> OK
price sack --> snail
weight (per kg or lb) --> probably snail

As an Admin:

• edit a shipping method
• on the calculator section choose one of the calculators marked with "snail" above
• click update
• type in an invalid value (e.g. some text or numbers with comma as separator)
• click update --> snail

Release notes

Changelog Category: User facing changes | Technical changes

The title of the pull request will be included in the release notes.

Dependencies

Documentation updates

[vsmay98]

This PR is ready for review.

[vsmay98]

Hello @drummer83
Could you please get this PR review?

[mkllnk]

This looks like a good solution. Can you fix the remaining Rubocop warning?

[vsmay98]

Done @mkllnk Please re-review

[jibees]

Thanks!

I'd squashed all of those 3 commits to avoid fix rubocop warning commit.

[drummer83]

Hi @vsmay98,
Thanks for this pull request!

I have first made sure that I can still reproduce the issue on our staging server.
Before your PR the situation was like this:

• flat percent --> snail
• flat rate (per order) --> OK
• flexible rate --> snail
• flat rate (per item) --> OK
• price sack --> snail
• weight (per kg or lb) --> snail

After your PR I tested again:

In the screen capture I always used the string 'invalid' as input but I have also tested:

• numbers with comma separator ✔️
• numbers with two '-' signs ✔️
• numbers with leading spaces, trailing spaces or spaces in between ✔️
• quotes ' and " ✔️

For the different calculators we now have:

• flat percent --> OK
• flat rate (per order) --> OK
• flexible rate --> OK
• flat rate (per item) --> OK
• price sack --> OK
• weight (per kg or lb) --> OK

Worth mentioning:

• For 'Flexible rate' the amount value is not validated as other fields, but it is set to '0' for invalid input while for 'Price sack' the amount values are validated as other fields - the error message is displayed for invalid input. Flexible rate should do the same.
• Invalid input field(s) should be highlighted (red border of input field) and all other updated information should be kept (including description, tags, display, ...)
• Flat rate (per order), Flexible rate, Flat rate (per item), Price sack: remove currency setting (the amount is considered the instance's currency anyway)

This is looking really great and it's removing quite a few snails at one shot. 💥

We are ready to go here and I will create a follow-up issue for the topics of 'worth mentioning' (probably later today). Maybe you would like to continue your great work on this! ➡️ #9836

Thanks again! 🥳